Electric Motor

ABSTRACT

An electric motor ( 1 ) including a stator ( 2 ), a rotor ( 3 ) having a field permanent magnet ( 6 ), a terminal block ( 21 ) fixed on the stator, and a magnetism detecting circuit for detecting magnetism of the field permanent magnet thereby to detect a rotational position of the rotor. The magnetism detecting circuit includes a circuit board ( 22 ) arranged on the terminal block, and a rotation sensor ( 30 ) mounted on the circuit board such that it is mounted in a sensor case ( 33 ). The sensor case ( 33 ) is so constituted as to position the rotation sensor ( 30 ) on he terminal block when the circuit board ( 22 ) is arranged on the terminal block.

TECHNICAL FIELD

The present invention relates to an electric motor provided with arotation sensor detecting a rotational position of a rotor.

BACKGROUND ART

Electric motors include a type in which motor coils are connected via aninsulating terminal block to an external circuit. In this type of motor,a rotational position detecting circuit is provided integrally in theterminal block so that efficiency in assembly of the terminal block tothe motor is improved. In this case, Hall elements serving as a rotationsensor and a heat sensitive element serving as a temperature sensor arefitted into element mounting portions after an electrically conductiveplate has been formed by insert molding in the forming of the terminalblock. A secondary formation is then carried out so that the rotationalposition detecting circuit is formed integrally. Japanese Patent No.3497684 discloses an electric motor constructed as described above, forexample.

DISCLOSURE OF THE INVENTION Problem to be Overcome by the Invention

In the above-described method, however, shrinkage of resin after theprimary formation sometimes reduces dimensional accuracy of each elementmounting portion. Reduction in the dimensional accuracy of each elementmounting portion results in reduction in the mounting accuracy of theHall elements, thereby reducing a detection accuracy of rotationalposition of the rotor.

An object of the present invention is to provide an electric motor inwhich accuracy in positioning the rotation sensor relative to theterminal block can be improved in an arrangement that motor coils areconnected via the terminal block to an external circuit.

Means for Overcoming the Problem

The present invention is an electric motor which comprises a stator, arotor having a field permanent magnet, a terminal block fixed to thestator, and a magnetism detecting circuit detecting magnetism of thefield permanent magnet, thereby detecting a rotational position of therotor, characterized in that the magnetism detecting circuit includes acircuit board provided in the terminal block and a rotation sensor whichis attached to the circuit board while being held by a sensor case, andthe sensor case includes a positioning portion the rotation sensorrelative to the terminal block when the circuit board has been providedin the terminal block.

Effect of the Invention

The magnetism detecting circuit can easily be mounted on the terminalblock since the magnetism detecting circuit comprises the circuit board.Furthermore, the rotation sensor can be positioned via the sensor caserelative to the terminal block easily and accurately only when thecircuit board is provided in the terminal block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a part of an electric motor of one embodimentin accordance with the present invention;

FIG. 2 is a longitudinal sectional side view of the motor;

FIG. 3 is a plan view of a terminal block assembly;

FIG. 4 is a longitudinal sectional side view of the terminal blockassembly;

FIG. 5 is a plan view of a sensor case; and

FIG. 6 is a longitudinal sectional side view of the sensor case.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in more detail with reference to theaccompanying drawings. FIGS. 1 to 6 illustrate one embodiment in whichthe invention is applied to a DC brushless motor of the outer rotor typefor driving a rotating tub of a washing machine, for example.

Referring to FIGS. 1 and 2, the motor 1 of the embodiment comprises astator 2 and a rotor 3. The rotor 3 includes a frame 4 made from amagnetic material into the shape of a shallow dish, an annular rotorcore 5 disposed along an inner circumferential surface of acircumferential wall of the frame 4, and magnetic field permanentmagnets 6 disposed on the inner circumference of the rotor core 5.Magnet insertion holes 7 are provided in the inner circumference of therotor core 5. The magnetic field permanent magnets 6 are inserted in themagnet insertion holes 7 respectively. The rotor core 5, the magneticfield permanent magnets 6 and the frame 4 are integrated by molded resin8 (shown only in FIG. 2). On a central part of the frame 4 is provided aboss 9 to be coupled to an end of a rotating tub shaft which is notshown.

The stator 2 includes a stator core 11 having a number of radiallyextending teeth 10, an insulating cover 12 covering the stator core 11and coils 13 wound on portions of the insulating cover 12 covering theteeth 10. Each coil 13 comprises three coil wires 13 a (shown only inFIG. 2).

The stator core 11 is made by stacking a plurality of steel sheets. Theinsulating cover 12 is made from a non-conductive synthetic resin andcomprises a pair of covering members sandwiching the stator core 11 fromboth axial sides.

A terminal block 15 and a terminal block assembly 16 are attached to anend face (hereinafter, “upper end face”) of both axial end faces of theinsulating cover 12 unopposed to the frame 4. The terminal block 15 andthe terminal block assembly 16 are provided so that ends of the coilwires 13 a are easily connected to an external circuit (not shown). Aplurality of engagement portions (partially shown in FIG. 2) areprovided on the upper end face of the insulating cover 12. Furthermore,the terminal block 15 and the terminal block assembly 16 have engagedportions 18 respectively. The engaged portions 18 are engaged with theengagement portions 17 respectively so that the terminal block 15 andthe terminal block assembly 16 are fixed to the insulating cover 12.

Furthermore, six rectangular cylindrical housing portions 19 (only onebeing shown in FIG. 2) are formed integrally in the portion of the upperend face of the insulating cover 12 to which portion the terminal block15 and the terminal block assembly 16 are attached. The housing portions19 are disposed along the inner circumference of the insulating cover12. One ends (terminal for external connection) of the respective coilwires 13 a are inserted into three of the six housing portions 19located under the terminal block 15.

The terminal block 15 is made from non-conductive synthetic resin. Threehousing portions 20 are formed integrally in a lower face of theterminal block 15 (a face opposed to the insulating cover 12). A commonconnection conductive plate (not shown) is embedded in the terminalblock 15. A connecting portion which is an end of the conductive plateprotrudes into the housings 20. When the terminal block 15 is attachedto the insulating cover 12, the housing 20 is adapted to be fitted withthe three housings 19 located higher as viewed in FIG. 1, whereby theconnecting portion and common connection terminal are electricallyconnected to each other.

Referring to FIGS. 3 and 4, the terminal block assembly 16 includes aterminal block 21 comprising a non-conductive synthetic resin and acircuit board 22 provided integrally on the terminal block 21. Theterminal block 21 includes a portion located on the insulating cover 12and a portion protruding from the insulating cover 12. Three housingportions 23 are formed integrally in the underside of a portion of theterminal block 21 located on the insulating cover 12 (surface opposed tothe insulating cover).

Three conductive plates 24 for external connection are embedded in theterminal block 21. The conductive plates 24 have respective one endsprovided with connecting portions (not shown) projecting into thehousing portions 23. When the terminal block assembly 16 has beenattached to the insulating cover 12, the housing portions 23 are adaptedto be fitted with the three housing portions 10 located lower as viewedFIG. 2, whereby the connecting portion and the external connectionterminals are electrically connected together.

A rectangular cylindrical connector 25 and a board housing portion 27are formed integrally on an outer circumferential upper surface of theportion of the terminal block 21 protruding from the insulating cover12. The board housing portion 27 is defined by a rectangular cylindricalhousing wall 26. The conductive plates 24 have the other ends located inthe connector 25. Accordingly, when a connector (not shown) of anexternal circuit is fitted into the connector 25, the three conductiveplates 24 are connected to the external circuit.

Furthermore, a rectangular plate-shaped circuit board 22 is housed inthe board housing portion 27. The housing wall 26 has an innercircumferential surface provided with a plurality of claws 26 a engaginga circumferential edge of the circuit board 22. Some of the claws 26 aengage one of sides of the circuit board 22 and the other claws 26 aengage the other side of the circuit board 22. The circuit board 22 isfixed in the board housing portion 27.

On the circuit board 22 are provided a magnetism detecting circuit (notshown) comprising a diode 28, a capacitor 29, Hall elements 30 servingas a rotation sensor, and the like. The diode 28 and the capacitor 29are provided on one side of the circuit board 22 and have respectivelead wires 28 a and 29 a soldered to the circuit board 22.

Furthermore, a connector 31 is provided on an end of one side of thecircuit board 22. An external connection conductive plate 32 has one endprotruding into the connector 31. The other end of the conductive plate32 is soldered to the circuit board 22. The housing wall 26 is providedwith a multiple wall 26 b located at both sides of the connector 31 whenthe circuit board 22 is placed in the circuit housing 27 and an opening26 c corresponding to an end of the connector 31.

An element case 33 (serving as a sensor case) made from a resin ismounted on an end of the other side of the circuit board 22 for thepurpose of holding the Hall elements 30. The element case 33 has twojuxtaposed housings 34 in which the Hall elements 30 are adapted to beheld therein as shown in FIGS. 5 and 6. The Hall elements 30 areprovided for detecting a rotational position of the rotor 3. The Hallelements 30 have lead wires 30 a soldered to the circuit board 22.

The element case 33 has a side which is opposed to openings of thehousings 34 and formed into a gentle arc face 33 a. A fitting protrusion35 is provided integrally on a central part of the mounting face of theelement case 33 which is mounted on circuit board 22. The fittingprotrusion 35 is inserted through a hole 36 (see FIG. 4) provided in thecircuit board 22 and comprises a pair of half-columns 35 a which aredisposed so as to become generally columnar. The hole 36 has an innerdiameter slightly smaller than an outer diameter of the whole fittingprotrusion 35. Accordingly, the protrusion 35 elastically deforms insuch a direction that the half-columns 35 a comes close thereto wheninserted through the hole 36. The protrusion 35 inserted through thehole 36 is thus prevented from falling out of the hole 36.

Furthermore, an engagement convexity 37 is provided on a central part ofa side of the element case 33 opposed to the mounting face of theelement case 33 which is mounted on circuit board 22. The board housing27 of the terminal block 22 has a bottom provided with a hole 38corresponding to the engagement convexity 37. The engagement convexity37 is adapted to engage the hole 38 when the circuit board 22 is placedin the board housing 27.

Potting of urethane 40 serving as a moisture-proof material is appliedin the board housing 27 to prevent the circuit board 22 from beingexposed.

An assembling procedure of the terminal block assembly 16 will now bedescribed. Firstly, the element case 33 is mounted to the circuit board22 on which the diode 28, the capacitor 29 and the like have beenmounted. More specifically, the fitting protrusion 35 of the elementcase 33 is fitted into the hole 36 of the circuit board 22. The Hallelements 30 are then inserted into the respective housings 34 of theelement case 33. The Hall elements 30 having been inserted in therespective housings 34 are held by engaging means (not shown) so as tobe prevented from falling out of the housings 34.

Subsequently, the circuit board 22 is placed in the board housing 27 ofthe terminal block 21 with the board side with the element case 33 beingplaced down so that the engagement convexity 3 engages the hole 38 ofthe board housing 27. In this case, the element case 33 is elasticallydeformed slightly such that the arc surface 33 a comes to a planar shapeand many parts of the arc surface 33 a strongly abut against the housingwall 26. FIG. 3 shows the arc surface 33 a before elastic deformation.However, as shown in FIG. 4, even after the elastic deformation, a smallgap is adapted to be defined between the arc surface 33 a and thehousing wall 26. More specifically, in the embodiment, the arc surface33 a serves as an abutting surface, and the housing wall 26 serves as apositioning wall. Furthermore, the positioning portion in the presentinvention is composed of the arc surface 33 a and the housing wall 26.As a result, the element case 33 is fixed to the terminal block 21, andthe Hall elements 30 held by the element case 33 are positioned relativeto the terminal block 21.

Subsequently, the board housing 27 is filled with urethane 40, which isthen hardened. Thus, the terminal block assembly 16 is constructed. Theurethane 40 has low viscosity although relatively less expensive. Sincethe multiple wall 26 b is provided in the embodiment, the urethane 40can be prevented from leaking from the opening 26 c.

According to the embodiment, the board housing 27 is provided in theterminal block, and the circuit board 22 having the magnetism detectingcircuit is provided in the board housing 27. Accordingly, the magnetismdetecting circuit can be provided in the terminal block 21 more easilyas compared with the conventional arrangement in which the conductiveplate constituting the magnetism detecting circuit is embedded in theterminal block.

Furthermore, the Hall elements 30 are held in the element case 33mounted on the circuit board 22. The circuit board 22 is then placed inthe board housing 27, whereby the Hall elements 30 are positionedrelative to the terminal block 21. Moreover, the engagement convexity 37provided on the element case 33 is caused to engage the hole 38, and thearc surface 33 a is caused to abut against the housing wall 26 so thatthe element case 33 is prevented from rattling, whereby the Hallelements 33 are positioned. Consequently, the Hall elements 30 can bepositioned relative to the terminal block 21 easily and accurately.

Furthermore, the element case 33 is provided with the fitting protrusion35 which is fitted into the hole 36 so that the element case 33 is fixedto the circuit board 22. Consequently, the working efficiency can beimproved when the element case 33 is mounted on the circuit board 22.

The present invention should not be limited to the foregoing embodimentbut may be modified or expanded within a range not departing from thegist.

INDUSTRIAL APPLICABILITY

As obvious from the foregoing, the motor of the present invention isuseful as a motor for driving a rotating tub in a washing machine, forexample, since the rotational position of the rotor can be controlledaccurately.

1. An electric motor which comprises: a stator (2); a rotor (3) having afield permanent magnet (6); a terminal block (21) fixed to the stator(2); and a magnetism detecting circuit detecting magnetism of the fieldpermanent magnet (6), thereby detecting a rotational position of therotor (3), characterized in that: the magnetism detecting circuitincludes a circuit board (22) provided in the terminal block (21) and arotation sensor (30) which is attached to the circuit board (22) whilebeing held by a sensor case (33); and the sensor case (33) includes apositioning portion the rotation sensor (30) relative to the terminalblock (21) when the circuit board (22) has been provided in the terminalblock (21).
 2. The motor of claim 1, further comprising a positioningwall (26) provided on the terminal block (21) and an engagement hole(38), wherein the positioning portion is provided in the sensor case(33) and includes an engagement convexity (37) engaging the engagementhole (38) when the circuit board (22) has been provided in the terminalblock (21), and an abutting surface (33 a) abutting the wall (26). 3.The motor of claim 1, further comprising a hole defined in the circuitboard (22) and a fitting protrusion (35) provided on the sensor case(33), wherein the sensor case (33) is constructed so as to be fixed tothe circuit board (22) when the fitting protrusion (35) is fitted in thehole (36).
 4. The motor of claim 1, further comprising a board housing(27) defined by a housing wall (26) in the terminal block (21), whereinthe board housing (27) is filled with a moisture-proof material (40)after the circuit board (22) has been housed therein.